Mechanisms of arm-tip regeneration in the sea star, Leptasterias hexactis

Abstract

Wound healing and regeneration following amputation of arm-tips of the sea star, Leptasterias hexactis, are described using light microscopy, SEM, TEM, and [H] thymidine autoradiography. The process can be divided into a number of stages. Initially, the wound is closed by contractions of the stump-tip. Re-epithelialization then occurs through migration of epidermal cells from adjacent areas over the wound to form a thin wound epidermis. This is converted into a thicker, permanent covering in concurrence with the onset of cell cycle activity in the wound epidermis and adjacent epidermal regions. Histolysis and phagocytosis of damaged tissues occur beneath the new epidermis and a small connective tissue scar develops at the wound site within which muscle differentiates. At this time, elevated levels of [H]thymidine incorporation are initiated in the sub-epidermal tissues of the arm-tip. A variety of differentiated cell types enter the cell cycle including cells of the parietal peritoneum, lining of the radial water canal, and the dermis. Cell division is accompanied by the development of a small new arm-tip complete with terminal ossicle, terminal tentacle, and optic cushion. The radial water canal, radial nerve, and perivisceral coelom extend by outgrowth into this newly developing tip. Accelerated growth of the regenerate then occurs in a zone just proximal to the new tip. There is no evidence of a blastema-like mass of rapidly dividing undifferentiated cells at the tip of regenerating arms. Arm-tip regeneration in this sea star may therefore be best described as a morphallactic-like process in which a true blastema is not formed, but in which scattered cell proliferation plays an essential role.

Patterns of bromodeoxyuridine incorporation and neuropeptide immunoreactivity during arm regeneration in the starfish Asterias rubens

“…The autoradiographic studies conducted on arm tip regeneration in the asteroid L. hexactis show a similar localization of labelled nuclei in wound and adjacent epidermal regions, parietal peritoneum and water canal epithelia (Mladenov et al 1989). This suggests that previous descriptions of a blastema in asteroid arm regrowth are due to misinterpretation of the area of cell debris and clotted coelomocytes which lie just proximal to the tip (Mladenov et al 1989). The BrdU experiments in the current study con¢rm the lack of such a centre of proliferation, although the accumulation of cells in the tip area may contribute to the regeneration.…”

“…Mladenov et al (1989) describe a thin layer of nervous tissue extending into the wound area of the regenerating arm tip of Lepasterias hexactis as early as 72 h PA. By 11 days there is a disorganized area of nerve distal to the nerve proper, probably corresponding to the di¡use nerve ¢bres shown by S1-IR in A. rubens. Neurosecretory cells are described in this area in L. hexactis, and also in association with the regenerating brachial nerve in the crinoid, Antedon mediterranea (Candia-Carnevali et al 1993).…”

“…Although many studies have centred on vertebrates (Holder 1988), there have also been numerous investigations of invertebrates, including the echinoderms which are able to undergo extensive regeneration (Hyman 1955;Mladenov et al 1989). Many species of echinoderms autotomize appendages, some are capable of evisceration, and some undergo asexual reproduction by ¢ssion; these phenomena all require a subsequent regenerative phase.…”

Myogenesis during holothurian intestinal regeneration

“…In crinoid arm regeneration, cell proliferation is active within the coelomic epithelia (Candia-Carnevali et al 1995). In starfish regenerating arms, active proliferation is also observed in epithelial structures of the water and perihemal canals, and these epithelia provide cells that migrate to the regenerating structure (Mladenov et al 1989;Moss et al 1998). Furthermore, our own studies and those of others have shown cell proliferation in the coelomic and luminal epithelia of sea cucumbers (Leibson 1992;García-Arrarás et al 1998).…”

Patterns and cellular mechanisms of arm regeneration in adult starfish Asterias rollestoni bell

“…Mladenov et al (1989) examined the arm-tip regeneration in starfish Leptasterias hexactis, and they reported that no blastema-like mass was found and described the arm-tip regeneration as a morphallactic-like process. Feder (1999) and Vickery et al (2001a) performed detailed research on the regeneration ability of starfish larva, and found that the starfish larva could completely regenerate the lost tissue structures and organs.…”